The present invention relates generally to the field of integrated circuit packaging and, more particularly, to multi-chip modules (MCMs) including embedded distributed power supply elements.
Integrated circuits (ICs), including signal ICs and microwave ICs are, to an ever increasing degree, being constructed employing various forms of multi-chip module (MCM) technology, including high density interconnect (HDI) technology. In an MCM, many chips, perhaps as many as one hundred, are interconnected in close proximity to each other.
The current requirements of such MCM are relatively great, for at least three reasons. First, in general, the power requirements of high performance chips are high. Second, operation at higher frequencies requires higher energies to switch semiconductor devices while driving the output capacitance. The power required is proportional to frequency. Third, integrated circuit chips inherently operate at relatively low voltages. Accordingly, for a given power level, the current required is relatively high, since power is equal to the product of voltage and current.
An integrated circuit might have as many as 20% of its input/output (IO) pads devoted to power and ground. Each of these pads must be connected to a current supply line, preferably at low inductance to minimize L(dI/dt) switching transients. Correspondingly, a typical prior art MCM will have many relatively high-inductance power supply and ground pins connected electrically in parallel in an effort to achieve an overall low impedance.
MCMs are increasingly being constructed employing a variety of integrated circuit and discrete components which represent differing technologies, such as complementary metal-oxide-semiconductor (CMOS), emitter coupled logic (ECL) silicon, and GaAs. Each technology has different voltage and current requirements. In the conventional approach, all power requirements are met by external power supplies and brought separately into the module through multiple pins. As power requirement become higher, more pins are required. However, pins are in short supply.
A particularly advantageous form of multi-chip module is a high density interconnect (HDI) structure which has been developed by General Electric Company. As disclosed in commonly-assigned Eichelberger et al. U.S. Pat. No. 4,783,695, issued Nov. 8, 1988, and related patents, the HDI structure offers many advantages in the compact assembly of digital and other electronic systems. For example, an electronic system which incorporates between thirty and fifty chips, or even more, can be fully assembled and interconnected on a single substrate which is fifty mm (two inches) long by fifty mm (two inches) wide by 1.27 mm (fifty mils) thick. One advantage of this HDI structure is that it provides a good heat sink for integrated circuit chips, including power and microwave chips, since an alumina substrate is employed. Further, as disclosed, for example, in commonly-assigned W. Kornrumpf et al. application Ser. No. 07/504,821, filed Apr. 5, 1990, now abandoned in favor of continuation application Ser. No. 07/869,090, filed Apr. 14, 1992, and allowed and entitled "HDI Microwave Circuit Assembly", the utility of the HDI structure has been extended from digital technology into the microwave regime.
Very briefly, in the manufacture of systems employing this HDI structure, individual cavities (or one large cavity) having appropriate depths at the intended locations of the various chips are formed in a component-supporting surface of the ceramic substrate. The various chips and other components are placed in their desired locations within the cavities, and adhesively attached.
At this stage, the upper surfaces of all components and portions of the substrate component-supporting surface are disposed in substantially a common plane. A multi-layer high density interconnect (HDI) overcoat structure including interleaved layers of dielectric material and metallized conductive material is then built up to electrically interconnect the components into a functioning system.
In previous systems employing HDI technology, the HDI overcoat structure typically does not extend all the way to the outer edge of the substrate component-supporting surface. Rather, the HDI overcoat structure terminates just inside a row of contact pads to which external connections are subsequently made, such as by ultrasonic wire bonding, when the system is finally assembled into a suitable leaded package. These contact pads are formed directly on portions of the substrate surface surrounding the cavities, and are electrically connected through suitable vias within the HDI overcoat structure to lower metallization layers of the HDI overcoat structure.
Power and ground plane metallization is also deposited directly on the ceramic substrate in some designs, for example to contact the back sides of the IC chips. (Metallization deposited or otherwise formed directly on the ceramic substrate, as opposed to metallization layers within the HDI overcoat structure, is referred to as "metal zero".) In some structures, power and ground plane layers are included in the HDI overcoat structure.